Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $200.91   13.513%   $228.059   $228.06   $228.05   $228.10  
  Purchase #2 $48.63   4.153%   $50.6496   $50.65   $50.65   $50.60  
  Purchase #3 $101.84   11.741%   $113.797   $113.80   $113.80   $113.80  
  Purchase #4 $77.82   8.675%   $84.5709   $84.57   $84.55   $84.60  
  Purchase #5 $53.76   11.377%   $59.8763   $59.88   $59.90   $59.90  
  Purchase #6 $124.65   13.705%   $141.7333   $141.73   $141.75   $141.70  
  Purchase #7 $249.46   8.753%   $271.2952   $271.30   $271.30   $271.30  
  7 purchase totals = $857.07       $949.9813   $949.99   $950.00   $950.00